Insulated gate bipolar transistor structure having low substrate leakage

ABSTRACT

A high voltage metal-oxide-semiconductor laterally diffused device (HV LDMOS), and more particularly an insulated gate bipolar junction transistor (IGBT), is disclosed. The device includes a semiconductor substrate, a gate structure formed on the substrate, a source and a drain formed in the substrate on either side of the gate structure, a first doped well formed in the substrate, and a second doped well formed in the first well. The gate, source, second doped well, a portion of the first well, and a portion of the drain structure are surrounded by a deep trench isolation feature and an implanted oxygen layer in the silicon substrate.

PRIORITY CLAIM

This is a divisional of U.S. application Ser. No. 14/967,676 and U.S.Pat. Nos. 8,575,694 and 9,214,547, all with an effective priority dateof Feb. 13, 2012. The disclosures of all are incorporated by referenceherein in their entirety.

FIELD

The present disclosure relates generally to semiconductor technology,and more particularly, to high voltage semiconductor devices and methodsof making the same.

BACKGROUND

Technological advances in semiconductor integrated circuit (IC)materials, design, processing, and manufacturing have enabledever-shrinking IC devices, where each generation has smaller and morecomplex circuits than the previous generation.

As semiconductor circuits composed of devices such asmetal-oxide-semiconductor field effect transistors (MOSFETs) are adaptedfor high voltage applications, such as high voltage lateral diffusionmetal-oxide-semiconductor devices (HV LDMOSs) including high voltageinsulated gate bipolar transistors (HV IGBTs), problems arise withrespect to decreasing voltage performance as the scaling continues withadvanced technologies. To prevent punch-through between source anddrain, or to reduce resistance of source and drain, standard MOSfabrication process flows may be accompanied by multiple implantationsof high concentrations. Substantial substrate leakage and voltagebreakdown often occurs with device reliability degradation.

Performance of a HV MOS transistor is often limited by its substrateleakage and breakdown voltage (BV) threshold. Substantial substrateleakage reduces switching speed and increases likelihood of unwantedlatch-up. Full or partial use of silicon-on-insulator (SOI) substrateshas been developed to reduce substrate leakage. Use of full SOIsubstrates is expensive and results in low BV threshold. Use of partialSOI substrates results in improved BV threshold, but is difficult andeven more expensive to make.

Therefore, a HV LDMOS device having a low substrate leakage and a highbreakdown voltage threshold and a method for making the same in a costeffective manner continues to be sought.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIGS. 1A and 1B are cross-sectional views of two types of conventionalhigh voltage lateral diffusion metal oxide semiconductor (HV LDMOS)transistor devices.

FIGS. 2A and 2B are cross-sectional views of two types of conventionalHV LDMOS transistor devices employing silicon-on-insulator (SOI)substrates.

FIG. 3 is a cross-sectional view of a HV LDMOS transistor according tovarious embodiments of the present disclosure.

FIG. 4 is an oxygen implant profile of the implanted oxygen layer in theHV LDMOS transistor according to various embodiments of the presentdisclosure.

FIG. 5 is a plot of a drain current versus a drain voltage during thetransistor operation for the HV LDMOS transistor according to variousembodiments of the present disclosure.

FIG. 6 is an electrical potential diagram modeled for the HV LDMOStransistor according to various embodiments of the present disclosure.

FIG. 7 is a plot of a drain current versus a drain voltage when thetransistor is in an off state according to various embodiments of thepresent disclosure.

FIG. 8 is a flow chart of a method for fabricating a HV LDMOS deviceaccording to various aspects of the present disclosure.

FIG. 9A to 9H are cross sections of a workpiece corresponding to HVLDMOS device embodiment of the present disclosure in various stages ofmanufacturing according to method embodiments of the present disclosure.

Various embodiments of the present invention will be explained in detailwith reference to the accompanying drawings.

DETAILED DESCRIPTION

The present disclosure relates to semiconductor high voltage lateraldiffusion metal oxide semiconductor (HV LDMOS) transistors having lowsubstrate leakage and high breakdown voltage thresholds and a method forfabricating such devices. It is understood that the following disclosureprovides many different embodiments, or examples, for implementingdifferent features of the invention. Specific examples of components andarrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. In addition, the present disclosure may repeat referencenumerals and/or letters in the various examples. This repetition is forthe purpose of simplicity and clarity and does not in itself dictate arelationship between the various embodiments and/or configurationsdiscussed. Moreover, the formation of a first feature over or on asecond feature in the description that follows may include embodimentsin which the first and second features are formed in direct contact, andmay also include embodiments in which additional features may be formedinterposing the first and second features, such that the first andsecond features may not be in direct contact.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper”, “over” and the like, may be used herein for ease of descriptionto describe one element or feature's relationship to another element(s)or feature(s) as illustrated in the figures. It will be understood thatthe spatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as being “below” or “beneath”other elements or features would then be oriented “above” the otherelements or features. Thus, the exemplary term “below” can encompassboth an orientation of above and below. The device may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein may likewise be interpretedaccordingly.

FIG. 1A is a cross-sectional view of a conventional HV LDMOS transistor.In FIG. 1A, an n-type HV MOS device 100 is fabricated in a p-substrate101. A deep n-well (n-drift) 102 is formed in the substrate 101. A fieldoxide 108 is formed over the n-well 102 and a gate 140 is partlyoverlying the field oxide 108. A source and a drain are formed onopposite sides of the gate 140. The source includes a pair of oppositelydoped regions p+ (132) and n+ (133) contained in a p-well 104. Sourceterminal 130 is electrically connected to the source regions 132 and133. On one side of gate 140 and at the edge of field oxide 108, n+doped drain region 120 is formed in n-well 102 and electricallyconnected to a drain terminal 120. A p-top region 105 is formed betweenfield oxide 108 and the deep implanted n-drift region 102. The p-topregion 105 is a floating layer and is not connected to the source or thedrain region.

FIG. 1B is a cross-sectional view of another conventional HV LDMOSdevice 150. Unlike device 100 in FIG. 1A, device 150 has the p-top layerreplaced by a buried p-well 155. In FIG. 1B, an n-type HV LDMOS device150 is fabricated in a p-substrate 151. A deep n-well (n-drift) 152 isformed in the substrate 151. A field oxide 158 is formed on the n-well152 and a gate 190 is partly overlying the field oxide 158. A source anda drain are formed on either side of the gate 190. The source includes ap-type region p+ (182) and an n-type region N+ (183), both contained ina p-well 154. Source terminal 180 is electrically connected to sourceregions 182 and 183. On the opposite side of gate 190 and at the edge offield oxide 158, n+ doped drain region 153 is formed in n-well 152 andis electrically connected to a drain terminal 170. A deep implantedregion p-well 155 is formed in the middle of the deep implanted n-driftregion 152 and is also under but not connected to field oxide 158. Theburied p-well region 155 is a floating layer and is not connected to thesource or the drain region.

In order to address the substantial substrate leakage current of theconventional HV LDMOS transistors of FIGS. 1A and 1B, an HV LDMOStransistor formed on a silicon-on-insulator (SOI) substrate is developedas shown in FIG. 2A. The HV LDMOS structure is formed over an SOIsubstrate including a buried oxide (BOX) layer 201. During operation,the BOX layer 201 limits the substrate leakage current. However, the HVLDMOS of FIG. 2A results in a very low breakdown voltage (BV) threshold(about ⅓ of the convention HV LDMOS of FIGS. 1A and 1B) because the BOXlayer 201 prevents the spread of a depletion region into the substrateby forming a layer of mobile charge under the BOX layer 201.

A partial SOI device of FIG. 2B is developed to increase the BVthreshold. In FIG. 2A, the BOX layer 201 does not extend under theentire device. A portion of the BOX layer 201 is removed and thesubstrate material re-formed under the drain structure 203 and then-well 205. In this partial SOI device, a voltage applied between thedrain and the substrate is supported across the BOX layer 201 and thedepletion layer into the substrate, which significantly improves thedevice BV threshold. However, the partial SOI device is difficult andvery expensive to make. One method of forming the partial SOI substrateinvolves etching through the p-substrate 207 from the backside to removea portion of the BOX layer 201 while leaving the substrate material onthe front side intact, then epitaxially growing the substrate materialback. Because the thickness of p-substrate, the amount of material toetch and regrow is very large compared to typical semiconductorprocesses and increases the cost of an SOI wafer, this method isdifficult to implement for mass-manufacturing. Another method of formingthe partial SOI substrate involves etching a portion of the BOX layerfrom the front side, depositing polysilicon over the BOX layer portions,and growing the monocrystalline substrate around the BOX layer and thepolysilicon. An anneal process then melts the polycrystalline areaswhile maintaining the structure in monocrystalline areas. A thermalgradient is then induced to allow recrystallization across thepolycrystalline area into a monocrystalline structure. This processresults in a non-planar top surface above the BOX layer which must thenbe planarized before further epitaxial process can proceed. Just as thebackside etch and regrowth method, this method is expensive anddifficult to implement for mass-manufacturing.

FIG. 3 shows a cross-sectional view of a HV LDMOS transistor 300according to various embodiments of the present disclosure. The HV LDMOSof FIG. 3 is a transistor having low substrate leakage and good BVthreshold without using expensive SOI substrates anddifficult-to-implement processes. The HV LDMOS 300 may be a high voltageinsulated gate bipolar transistors (HV IGBT). In FIG. 3, a lightly dopedsubstrate 301 having a first type of conductivity is provided. In thepresent embodiment, the HV LDMOS transistor 300 is an n-type HV LDMOS,and thus, the substrate 301 includes a p-type silicon substrate(p-substrate). The substrate be a semiconductor wafer, such as a siliconwafer. Alternatively or additionally, the substrate may include othersemiconductors, such as germanium, silicon carbide, gallium arsenic,indium arsenide, and indium phosphide. The substrate may include analloy semiconductor, such as silicon germanium, silicon germaniumcarbide, gallium arsenic phosphide, and gallium indium phosphide.

A process such as separation by implanted oxygen (SIMOX) is used tocreate an implanted oxygen layer 303 below a top surface 305 of thesubstrate 301. The implanted oxygen layer 303 does not affect theplanarity of the top surface 305 of the substrate 301. A first well 307is formed over the substrate 301, the first well having a different typeof conductivity from the substrate. For example, the substrate has ap-type conductivity and the first well has an n-type conductivity. Inthe present embodiment, the first well 307 is an N-Drift (n-well) formedover the p-substrate 301 by an epitaxial process using a dopant.

A second well 309 is formed in the first well 307, the second well 309having the same type of conductivity as the substrate 301. The secondwell 309 may be referred to as a P-body. The second well 309 may havedifferent portions, each portion having a different location and depthin the first well 307 from the other portions. The two portions areformed in separate doping processes. For example, shown in FIG. 3, thesecond well P-Body 309 has a portion 309 a, which surrounds sourceregions 324 and 326, and another portion 309 b, which extends out fromthe portion 309 a in a direction towards the drain structure 328 and330. Portion 309 a and portion 309 b of the P-Body are attached. TheN-Drift 307 has an n-type dopant such as phosphorus, and the P-Body 309have a p-type dopant such as boron. In one embodiment, the N-Drift 307and P-Body 309 may be formed by a plurality of processing steps, whethernow known or to be developed, such as growing a sacrificial oxide on thesubstrate, opening a pattern for the location(s) of the P-Body regions309 a and 309 b or N-Drift 307, and implanting the impurities.

A field insulating layer 308 is formed on the substrate. A gatestructure 345 and 340 has a first portion overlying the first wellN-Drift 307 and a second portion overlying the second well P-Body 309.The gate structure includes a gate dielectric 340 and a gate electrode345 formed on the gate dielectric 340. The gate dielectric 340 mayinclude a silicon oxide layer suitable for high voltage applications.Alternatively, the gate dielectric 340 may optionally include a high-kdielectric material, silicon oxynitride, other suitable materials, orcombinations thereof. The high-k material is selected from metal oxides,metal nitrides, metal silicates, transition metal-oxides, transitionmetal-nitrides, transition metal-silicates, oxynitrides of metals, metalaluminates, zirconium silicate, zirconium aluminate, hafnium oxide, orcombinations thereof. The gate dielectric 340 may have a multilayerstructure, such as one layer of silicon oxide and another layer ofhigh-k material. The gate dielectric 340 may be formed using chemicalvapor deposition (CVD), physical vapor deposition (PVD), atomic layerdeposition (ALD), thermal oxide, other suitable processes, orcombinations thereof.

The gate electrode 345 is coupled to metal interconnects 316 anddisposed overlying the gate dielectric 340. In some embodiments, thegate electrode 345 includes a doped or non-doped polycrystalline silicon(or polysilicon). Alternatively, the gate electrode layer 345 include ametal, such as Al, Cu, W, Ti, Ta, TiN, TaN, NiSi, CoSi, other suitableconductive materials, or combinations thereof. The gate electrode layer345 are formed by CVD, PVD, ALD, plating, or other processes. The gateelectrode layer may have a multilayer structure and may be formed in amultiple-step process.

A drain structure 328 and 330 is formed in the first well N-drift 307and connected to drain interconnect 314 from above. The drain structure328 and 330 are located across the field oxide 308 from the gatestructure 340 and 345. A source structure 324 and 326 is formed in thetop surface of an upper portion 309 a of the second well P-Body 309,across the gate structure 340 and 345 from the drain structure 328 and330. In some embodiments, the source has two oppositely doped regions324 and 326, both formed in the top surface of the upper portion 309 aof the second well P-Body 309 and both connected to source interconnect318 from above. A first region of the source 326 and the drain structure330 may have the first type of conductivity, which is the same as thatof the substrate 301. A second region of the source 324 and the drainstructure 328 may have the second type of conductivity, which is thesame as the first well 307. For example in FIG. 3, the first region ofthe source 324 and the drain structure 328 include n-type dopants, suchas phosphorous or arsenic, and the second region of the source 326 andthe drain structure 330 include p-type dopants, such as boron. Thesource structure and drain structure may be formed by a method, such asion implantation or diffusion. A rapid thermal annealing (RTA) processmay be used to activate the implanted dopants.

A deep trench isolation (DTI) 311 laterally surrounds the gate structure340 and 345, the source structure 324 and 326, the second well P-body309, the field oxide 308, and the drain structure 330 in the first well307. Note that the drain structure 328 is not surrounded by the DTI 311.The DTI feature connects to the implanted oxygen layer 303 to pocketcertain features of HV LDMOS 300 within insulating materials DTI 311 andimplanted oxygen layer 303. The DTI feature 311 is a dielectricmaterial. In certain embodiments, the DTI feature 311 is about 100 nm ormore wide. The DTI feature 311 may include a thermally grown siliconoxide layer formed on sidewalls of a trench and the trench filled withthermally grown or deposited silicon oxide. For example, the DTI 311 maybe filled with silicon oxide from a CVD process such as high densityplasma (HDP) CVD.

FIG. 4 is an oxygen implant profile of the implanted oxygen layer 303 inthe substrate 301. As measured from the top surface 305 of the substrate301, the implanted oxygen layer 303 has an oxygen concentrationdistribution with a peak oxygen concentration 401 at about 300 nm, orbetween about 200 nm to 400 nm from the top surface 305. A thickness 403of the implanted layer 303 defined as a portion below the top surfacewith oxygen concentration above a predetermined amount. For example, theimplanted layer thickness may be about 100 nm with oxygen concentrationabove about 5E20. The implanted layer is at least 100 nm below the topsurface 305, and may be between about 150 nm to about 450 nm. Dependingon the implant energy and duration, the implanted layer may be madethinner or thicker. Note that portion 405 of the implant profile nearthe top surface at about 0 to about 75 nm is surface noise and does notreflect the implanted oxygen concentration.

FIG. 5 is a plot of current versus drain voltage during the transistoroperation when the gate voltage is 20 volts. In other words, thetransistor is turned on for conduction between the source and the drain.Line 501 is the drain current in amps per micrometer versus drainvoltage. Line 501 shows a normal operation of the transistor where thedrain current increases as the drain voltage increases. The currentincrease is almost linear during the high voltage operation regions ofabout 150 volts to about 200 volts at the drain. Line 503 shows thesubstrate current in a log scale in amps per micrometer during the sameoperation. While the substrate current, in other words, the undesirablesubstrate leakage current, increases slightly over the operating rangeof the drain voltages, it is kept below about 2 Log-11 at all times.Line 503 shows negligible substrate leakage during the transistoroperation. Thus, minimal current escapes the transistor of the presentdisclosure during operation such that reduced power and reducedlikelihood of latch-up and other undesirable phenomenon would occur.

FIG. 6 is an electrical potential diagram modeled for the HV LDMOStransistor 300 when a high voltage of 856.6 volts is applied to thedrain (top left of FIG. 6). Because of the drain being separated intoportions 328 and 330, the high voltage potential spreads across thesubstrate instead of being confined within the pocket of DTI 311 andimplanted oxygen layer 303. The use of drain structure 328 allows the HVLDMOS transistor 300 to have a much higher breakdown voltage because thepotential lines spread into the silicon substrate.

FIG. 7 shows the drain current versus a drain voltage with a gatevoltage of 5 volts when the transistor is in an off state. Theresistance between the source and drain is about 40 mega ohms percentimeter squared. Line 701 shows the drain current in E-10 amps permicrometer. The drain current increased slightly until over 800 volts isapplied and breakdown threshold is indicated at 862 volts. Thisbreakdown threshold is much higher than a transistor that does notinclude the separated drain structure 328, for example, as compared tothe transistor of FIG. 2A that has a reported breakdown voltage of 163volts. This breakdown voltage is also higher than the partial SOItransistor of FIG. 2B that has a reported breakdown voltage of 499volts.

FIG. 8 is a flowchart of a method 800 for fabricating a high voltagelaterally diffused MOS semiconductor device, according to variousaspects of the present disclosure. It should be noted that the method800 may be implemented in a complementary metal oxide semiconductor(CMOS) technology process flow. Accordingly, it is understood thatadditional processes may be provided before, during, and after themethod 800, and some processes may only be briefly described herein.

The method 800 begins with block 801 in which a semiconductor substrateis provided. The substrate has a first type of conductivity. Forexample, as shown in FIG. 9A, the substrate may be p-type as a substrate901. In various examples, the substrate 901 is a lightly doped silicon.The method 800 continues at block 803 in which oxygen is implanted intothe lightly doped semiconductor substrate below a top surface of thesubstrate. FIG. 9B shows the substrate 901 with an implanted oxygenlayer 903 below a top surface of the substrate 901. The substrate 901 ispatterned first to protect areas not intended to be exposed to oxygenimplantation. Then oxygen is implanted into the substrate at least about100 nm from the top surface. Relatively high dosage is used to achievean oxygen peak about 1E21 atoms per cubic centimeter or greater. The topsurface remains flat for subsequent epitaxial processes. Afterimplanting, the patterning is removed to result in the workpiece asdepicted in FIG. 9B.

In operation 805 of FIG. 8, a first well region is formed having asecond type of conductivity, which is different from the first type ofconductivity of the substrate. As shown in FIG. 9C, for example, a firstwell 905 may be an n-well, such as the n-well (N-Drift) formed over thep-substrate 901. The first well 905 may be epitaxially grown over thesubstrate using epitaxial processes known in the art with insitu dopingor a doping step may be later performed using implantation or thermaldiffusion methods. For example, the first well 905 may be about 4micrometers thick, or between about 2 and about 5 micrometers thick.

The method 800 continues with block 807 in which a second well region isformed in the first well region. FIG. 9D shows the workpiece after block807. FIG. 9D shows a second well region 907 in the first well region905. The second well region 907 may be formed in two operations. A firstportion 907 a of a second well 907 is formed first in the first well905. The first portion 907 a of the second well 907 starts from a topsurface of the first well 905 and extends down in the first well 905. Asecond portion 907 b of the second well 907 is formed in the first well905; this second portion 907 b extends laterally from the first portion907 a beyond the top surface of the first portion 907 a of the secondwell below the top surface of the first well 905. The first and secondportions of the second well 907 a and 907 b have the first type ofconductivity. For example, the second well is p-type doped. The firstportion and the second portion of the second well 907 a and 907 b areformed by implanting a p-type dopant using different patterns. Eitherone may be formed first using a first pattern, then the other may beformed using a second pattern. The implantation uses substantially thesame dopant concentrations at different implantation energy levels toachieve varying depths. As shown in FIG. 9D, the resulting second wellhas a boot shape, but other variations are possible. For example, thesecond well may be an inverted T.

The method 800 continues with block 809 in which an insulating layer,also referred to as a field oxide, is formed on the workpiece. The fieldoxide may include a dielectric, such as silicon oxide, nitride, or othersuitable insulating materials. FIG. 9E shows an example of a field oxide909 formed over and in the first well 905 next to but not adjoiningsecond well 907. The field oxide 909 may be formed by a thermal oxideprocess. The workpiece is patterned to protect regions where the fieldoxide is undesirable and subjected to a high temperature, for example,about 800 degrees Celsius, in the presence of oxygen.

In the next block 811 of FIG. 8, a deep trench isolation (DTI) featureis formed. In FIG. 9E, a DTI feature 911 laterally surrounds the fieldoxide 909 and second well 907 in the first well 905 and connects to theimplanted oxygen layer 903. The DTI 911 and the implanted oxygen layer903 surround various elements of the HV LDMOS and isolate these variouselements from the substrate and other devices. In some embodiemtns, theDTI 911 contacts the implanted oxygen layer where oxygen concentrationis greater than about 1E20. The DTI feature 911 is formed by etching adeep trench using an etch mask, which may be a photomask or a hardmask,and then filling the deep trench with insulating material. In oneexample, the insulating material is thermally grown silicon oxide, whichis the same material as that of the field oxide. The DTI material may begrown at the same time or at different time from the field oxide 909. Inone example, the deep trench is etched first before the field oxide isformed, then the workpiece is repatterned to expose the field oxideregion and the trenches. The silicon oxide insulator is grown in thedeep trench and over the exposed portions of the first well 905 at thesame time. The silicon oxide would fill the deep trenches first andclose the opening while the field oxide 909 continues to grow. Inanother example, a thin layer of thermally grown silicon oxide is formedfirst on the deep trench sidewalls and bottom, then the deep trench isfill with plasma-assisted deposition process such as high density plasma(HDP) CVD.

Referring back to FIG. 8, in operation 813, a gate structure is formedover the workpiece. As shown in FIG. 9F, a gate structure 913 has alower dielectric layer 913 a and an upper electrode layer 913 b. Thegate structure 913 may overlie three areas: a first part of the gatestructure 913 overlies an edge of the field oxide 909, a second part ofthe gate structure overlies the top surface of the first well 905, andthe third part of the gate structure overlies the first portion 907 a ofthe second well 907. The precise overlay of the gate structure 913 ofthe three areas is achieved by a process including photolithographypatterning and etching. One exemplary method for patterning the gatedielectric and electrode layers over the three areas is described below.A layer of photoresist is formed on a polysilicon electrode layer by asuitable process, such as spin-on coating, and then patterned to form apatterned photoresist feature by a proper lithography patterning method.The pattern of the photoresist can then be transferred by a dry etchingprocess to the underlying polysilicon electrode layer and the gatedielectric layer to form a gate electrode and a gate dielectric, in aplurality of processing steps and various proper sequences. The preciseoverlay of the gate structure of the field oxide, the first well, andthe second well is controlled by the lithographic alignment procedure.The photoresist layer is stripped thereafter. In another embodiment,only the gate electrode layer is patterned. In another embodiment, ahard mask layer is formed on the polysilicon layer. The patternedphotoresist layer is formed on the hard mask layer. The pattern of thephotoresist layer is transferred to the hard mask layer and thentransferred to the polysilicon layer to form the gate electrode. Thehard mask layer may include silicon nitride, silicon oxynitride, siliconcarbide, and/or other suitable dielectric materials, and may be formedusing a method such as CVD or PVD.

Referring back to FIG. 8, the method 800 continues with block 815, inwhich a source region and a drain region are formed. As shown in FIG.9G, a source region 915 includes two regions 915 a and 915 b. The firstsource region 915 a may have the first type of conductivity; a secondsource region 915 b, formed next to the first source region 915 a, mayhave the second type of conductivity. For example, the first part sourceis p-type, and the second part source is n-type or vice versa. The drainregion 917 includes two regions 917 a and 917 b. The first drain region917 a may have the first type of conductivity; a second drain region 917b, formed next to the first source region 917 a across the DTI feature911, may have the second type of conductivity. For example, the firstpart source is p-type, and the second part source is n-type or viceversa. The first and second source and drain regions are formed byimplanting n-type or p-type or both types of dopants in each of theregions. Portions of the regions may be implanted at the same time. Inone example, regions 917 a and 915 b are implanted at the same time; andregions 917 b and 915 a are implanted at the same time. In anotherexample, all of the regions are implanted using one type of dopant andonly two regions are implanted using another type of dopant. In stillother examples, the regions are implanted at different times.

Referring back to FIG. 8, interconnect structures are formed over thetransistor. As shown in FIG. 9H, interconnect structures 919, 921, and923 are formed over various features of the transistor. Note thatinterconnect structure 919 has two parts, one part connecting to each ofthe drain structure regions 917 a and 917 b. Interconnect structure 921connects to the gate structure 913. Interconnect structure 923 connectsto the source regions 915 a and 915 b singly or together. Each of theinterconnect structures 919, 921, and 923 includes a contact portionthat directly contacts the transistor element and an interconnectportion above the contact portion. In one embodiment, an interlayerdielectric (ILD) and a multilayer interconnect (MLI) structure areformed in a configuration such that the ILD separates and isolates eachmetal layer from other metal layers. In furtherance of the example, theMLI structure includes contacts, vias and metal lines formed on thesubstrate. In one example, the MLI structure may include conductivematerials, such as aluminum, aluminum/silicon/copper alloy, titanium,titanium nitride, tungsten, polysilicon, metal silicide, or combinationsthereof, being referred to as aluminum interconnects. Aluminuminterconnects may be formed by a process including physical vapordeposition (or sputtering), chemical vapor deposition (CVD), orcombinations thereof. Other manufacturing techniques to form thealuminum interconnect may include photolithography processing andetching to pattern the conductive materials for vertical connection (viaand contact) and horizontal connection (conductive line). Alternatively,a copper multilayer interconnect is used to form the metal patterns. Thecopper interconnect structure may include copper, copper alloy,titanium, titanium nitride, tantalum, tantalum nitride, tungsten,polysilicon, metal silicide, or combinations thereof. The copperinterconnect may be formed by a technique including CVD, sputtering,plating, or other suitable processes.

The ILD material includes silicon oxide. Alternatively or additionally,the ILD includes a material having a low dielectric constant, such as adielectric constant less than about 3.5. In one embodiment, thedielectric layer includes silicon dioxide, silicon nitride, siliconoxynitride, polyimide, spin-on glass (SOG), fluoride-doped silicateglass (FSG), carbon doped silicon oxide, Black Diamond® (AppliedMaterials of Santa Clara, Calif.), Xerogel, Aerogel, amorphousfluorinated carbon, Parylene, BCB (bis-benzocyclobutenes), SiLK (DowChemical, Midland, Mich.), polyimide, and/or other suitable materials.The dielectric layer may be formed by a technique including spin-on,CVD, or other suitable processes.

MLI and ILD structure may be formed in an integrated process such as adamascene process. In a damascene process, a metal such as copper isused as conductive material for interconnection. Another metal or metalalloy may be additionally or alternatively used for various conductivefeatures. Accordingly, silicon oxide, fluorinated silica glass, or lowdielectric constant (k) materials can be used for ILD. During thedamascene process, a trench is formed in a dielectric layer, and copperis filled in the trench. Chemical mechanical polishing (CMP) techniqueis implemented afterward to etch back and planarize the substratesurface.

Among various embodiments, the present structure provides an enhancedperforming high voltage device, configured as a lateral diffused MOS (HVLDMOS) formed in a dual-well structure (an extended p-type well insidean n-type well) within the substrate and surrounded in an insulatingpocket, which reduces substrate leakage current to almost zero. Aseparate portion of the drain region is outside of the insulating pocketsuch that the substrate is available for electric potential lines duringwhen a high drain voltage is applied.

An aspect of this description relates to a high voltage semiconductortransistor comprising a lightly doped semiconductor substrate having afirst type of conductivity. A portion of the lightly doped semiconductorsubstrate includes an implanted oxygen layer below a top surface of thelightly doped semiconductor substrate. The high voltage semiconductortransistor also comprises a first well region having a second type ofconductivity and formed over the lightly doped semiconductor substrate.The high voltage semiconductor transistor further comprises a secondwell region in the first well region and having the first type ofconductivity. The high voltage semiconductor transistor additionallycomprises an insulating structure over and partially embedded in thefirst well region and not contacting the second well region.

The high voltage semiconductor transistor also comprises a gatestructure near the insulating structure over the first well region. Thehigh voltage semiconductor transistor further comprises a drain regionin the first well region across the insulating structure from the gatestructure. The high voltage semiconductor transistor additionallycomprises a source region in the second well region disposed on a sideof the gate structure opposite from the drain region. The high voltagesemiconductor transistor also comprises a deep trench isolation featurein the first well region surrounding the second well region, theinsulating structure, the gate structure, the source region, and a firstdrain portion, wherein the deep trench isolation feature contacts theimplanted oxygen layer.

Another aspect of this description relates to a method for fabricating ahigh voltage semiconductor transistor comprising implanting oxygen intoa lightly doped semiconductor substrate having a first type ofconductivity, the oxygen being implanted below a top surface to form animplanted oxygen layer. The method also comprises forming a doped firstwell region over the substrate, the first well region having a secondtype of conductivity different from the first type of conductivity. Themethod further comprises forming a first doped portion of a second wellregion in the first well region, the first doped portion occupying aregion starting from a top surface of the first well region andextending down into the first well region. The method additionallycomprises forming a second doped portion of the second well region inthe first well region, the second doped portion extending laterally fromthe first doped portion toward a drain region, and both the first andsecond portions having the first type of conductivity.

The method also comprises forming an insulating layer on the substrate.The method further comprises forming a gate structure on the substrate,the gate structure having a first part overlying the insulating layer, asecond part overlying the first well region, and a third part overlyingthe first doped portion of the second well region. The methodadditionally comprises forming a source region in the first dopedportion of the second well region on an opposite side of the gatestructure from the insulating layer. The method also comprises formingthe drain region in the first well region. The method additionallycomprises forming a deep trench isolation feature in the substrate andthe first well region, wherein the deep trench isolation featuresurrounds the second well region, a first portion of the drain regionand the insulating layer, and contacts the implanted oxygen layer.

The foregoing has outlined features of several embodiments. Thoseskilled in the art should appreciate that they may readily use thepresent disclosure as a basis for designing or modifying other processesand structures for carrying out the same purposes and/or achieving thesame advantages of the embodiments introduced herein. Those skilled inthe art should also realize that such equivalent constructions do notdepart from the spirit and scope of the present disclosure, and thatthey may make various changes, substitutions and alterations hereinwithout departing from the spirit and scope of the present disclosure.

What is claimed is:
 1. A high voltage semiconductor transistor,comprising: a semiconductor substrate having an implanted oxygen layer;a first well region; an insulating structure; a gate structure near theinsulating structure over the first well region; a drain region in thefirst well region across the insulating structure from the gatestructure, wherein the drain region comprises a first drain portion anda second drain portion; a source region disposed on a side of the gatestructure opposite from the drain region; and an isolation feature inthe first well region, the isolation feature at least partiallysurrounding the insulating structure, the gate structure, the sourceregion, and the first drain portion, wherein a portion of the isolationfeature is closer to the drain region than the source region, whereinthe first drain portion is separated from the second drain portion bythe isolation feature and, wherein the isolation feature is proximate tothe implanted oxygen layer.
 2. The transistor of claim 1, wherein thesemiconductor substrate is lightly doped having a first type ofconductivity, wherein a portion of the lightly doped semiconductorsubstrate includes the implanted oxygen layer below a top surface of thelightly doped semiconductor substrate.
 3. The transistor of claim 2,wherein the first well region has a second type of conductivity and isformed over the lightly doped semiconductor substrate.
 4. The transistorof claim 3, further comprising: a second well region in the first wellregion and having the first type of conductivity.
 5. The transistor ofclaim 4, wherein the insulating structure is over and partially embeddedin the first well region and not contacting the second well region. 6.The transistor of claim 4, wherein the source region is in the secondwell region.
 7. The transistor of claim 4, wherein the isolation featureis a deep trench isolation feature and at least partially surrounds thesecond well region.
 8. The transistor of claim 2, wherein the implantedoxygen layer has a peak oxygen concentration at about 300 nm from thetop surface of the lightly doped semiconductor substrate.
 9. Thetransistor of claim 1, wherein the implanted oxygen layer includesoxygen concentration above about 5E20 atoms/cm³ and is about 100 nmthick.
 10. The transistor of claim 2, wherein the implanted oxygen layeris at least 100 nm below the top surface of the lightly dopedsemiconductor substrate.
 11. The transistor of claim 1, wherein thesource region comprising a first region having the first type ofconductivity and a second region having the second type of conductivity.12. The transistor of claim 7, wherein the deep trench isolation featurecontacts the implanted oxygen layer where oxygen concentration isgreater than about 1E20 atoms/cm³.
 13. The transistor of claim 7,wherein the deep trench isolation feature comprises thermally grownsilicon oxide.
 14. The transistor of claim 7, wherein the deep trenchisolation feature is at least 100 nm wide.
 15. The transistor of claim4, wherein the second well region comprises a first portion and a secondportion, the first portion surrounding the source region and the secondportion extending laterally under the gate structure.
 16. The transistorof claim 1, wherein the gate structure comprises a gate electrode, thegate electrode comprising Al, Cu, W, Ti, Ta, TiN, TaN, NiSi, CoSi, or acombination thereof.
 17. The transistor of claim 1, wherein the gatestructure comprises a gate dielectric, the gate dielectric comprisingsilicon oxide, a high-K dielectric material, or silicon oxynitride. 18.The transistor of claim 1, wherein the gate structure is formed partlyon the insulating structure.
 19. A high voltage semiconductortransistor, comprising: a semiconductor substrate; a first well regionover the semiconductor substrate; a second well region in the first wellregion; an insulating structure over and partially embedded in the firstwell region, the insulating structure isolated from contact with thesecond well region; a gate structure near the insulating structure overthe first well region; a drain region in the first well region acrossthe insulating structure from the gate structure, wherein the drainregion comprises a first drain portion adjacent to the insulatingstructure and a second drain portion farther away from the insulatingstructure; a source region in the second well region disposed on a sideof the gate structure opposite the drain region; and a trench isolationfeature in the first well region, the trench isolation feature beingproximate to an implanted oxygen layer, wherein the first drain portionis separated from the second drain portion by a portion of the trenchisolation feature, and wherein the trench isolation feature surroundsone or more of the second well region, the insulating structure, thegate structure, the source region, and the first drain portion.
 20. Ahigh voltage semiconductor transistor, comprising: a semiconductorsubstrate; a first well region over the semiconductor substrate; asecond well region in the first well region; an insulating structureover and partially embedded in the first well region, the insulatingstructure isolated from contact with the second well region; a gatestructure partly on the insulating structure over the first well region;a drain region in the first well region across the insulating structurefrom the gate structure, wherein the drain region comprises a firstdrain portion adjacent to the insulating structure and a second drainportion farther away from the insulating structure; a source region inthe second well region disposed on a side of the gate structure oppositethe drain region; and a trench isolation feature in the first wellregion, the trench isolation feature being proximate to an implantedoxygen layer, wherein the first drain portion is separated from thesecond drain portion by a portion of the trench isolation feature, andwherein the trench isolation feature and the implanted oxygen layertogether surround one or more of the second well region, the insulatingstructure, the gate structure, the source region, and the first drainportion.